            :times-solved 0
            :description "Given a string of comma separated integers, write a function which returns a new comma separated string that only contains the numbers which are perfect squares."
            :tags ["medium"]
+	   :approved true
            :tests ["(= (__ \"4,5,6,7,8,9\") \"4,9\")"
 		   "(= (__ \"15,16,25,36,37\") \"16,25,36\")"]}) 
 


      
      (insert! :problems
           {:_id 78
            :title "Reimplement Trampoline"
            :times-solved 0
            :restricted ["trampoline"]
            :description "Reimplement the function described in <a href=\"76\"> \"Intro to Trampoline\"</a>."
            :approved true
            :tags ["medium" "core-functions"]
            :tests ["(= (letfn [(triple [x] #(sub-two (* 3 x)))\n          (sub-two [x] #(stop?(- x 2)))\n          (stop? [x] (if (> x 50) x #(triple x)))]\n    (__ triple 2))\n  82)"
                    "(= (letfn [(my-even? [x] (if (zero? x) true #(my-odd? (dec x))))\n          (my-odd? [x] (if (zero? x) false #(my-even? (dec x))))]\n    (map (partial __ my-even?) (range 6)))\n  [true false true false true false])"]})

      (insert! :problems
           {:_id 79
            :title "Power Set"
            :times-solved 0
            :description "A power set is the set of all subsets of a given set. Given a list, produce a set of sublists while preserving the order of elements."
            :approved true
            :tags ["hard" "seqs"]
            :tests ["(= (__ '(1 :a)) '#{(1 :a) (:a) () (1)})"
                    "(= (__ '()) '#{()})"
                    "(= (__ '(1 2 3)) '#{() (1) (2) (3) (1 2) (1 3) (2 3) (1 2 3)})"

           :times-solved 0
           :description "A <a href=\"http://en.wikipedia.org/wiki/Tic-tac-toe\">tic-tac-toe</a> board is represented by a two dimensional vector. X is represented by :x, O is represented by :o, and empty is represented by :e.  A player wins by placing three Xs or three Os in a horizontal, vertical, or diagonal row.  Write a function which analyzes a tic-tac-toe board and returns :x if X has won, :o if O has won, and nil if neither player has won."
           :tags ["medium" "game"]
	   :approved true
           :tests ["(= nil (__ [[:e :e :e]\n            [:e :e :e]\n            [:e :e :e]]))"
		   "(= :x (__ [[:x :e :o]\n           [:x :e :e]\n           [:x :e :o]]))"
		   "(= :o (__ [[:e :x :e]\n           [:o :o :o]\n           [:x :e :x]]))"
